1. Field of the Invention
The present invention relates to digital media, and more particularly to digital media such as cards and modules, sockets therefor, control thereof, and combinations thereof.
2. Description of Related Art
A variety of add-on cards and modules for use in digital systems such as personal computers ("PC") have enjoyed a measure of success in various memory-intensive applications. Some of these memory add-on cards use flash memory, and are known as flash PC cards. Flash PC cards have become widely used for mass data storage applications, and are a popular alternative for conventional add-on card implemented non-volatile memory solutions such as rotating hard disks and battery-backed SRAM, especially for notebook computers, personal data assistants ("PDAs"), and some high-end digital cameras. As an alternative to rotating hard disk PC cards, flash PC cards are more rugged and space efficient, are silent, consume less power, provide higher performance (in most cases), and provide a removable form-factor. As an alternative to battery-backed SRAM PC cards, flash PC cards typically offer higher-densities and lower cost per bit and are not as limited by reliability and temperature issues associated with batteries used in the battery-backed SRAM PC cards.
FIG. 1 shows to scale the surface area of a number of high capacity memory card types presently available. The surface area of a flash PC card is shown at 100 in FIG. 1. Flash PC cards are compliant with the Personal Computer Memory Card International Association ("PCMCIA") standard, which specifies a form factor of approximately 85.6 mm (3.37 inches) by 54 mm (2.126 inches), with a thickness of either about 3 mm for a Type-I card or about 5 mm for a Type-II card. The connector specified by the PCMCIA standard uses 68 pins organized in two rows of 34 pins each with 1.27 mm (50 mils) spacing between pins. The physical specifications for PC cards are described in a publication of the Personal Computer Memory Card International Association/JEIDA entitled PC Card Standard, Volume 3: Physical Specification, Document No. 0295-03-1500, February 1995.
Flash PC cards typically have a high memory capacity of from about 2 Megabytes to 85 Megabytes, although recently even higher capacity cards have been introduced. Like hard-disks, flash PC cards spend about 75 percent of operation time being read from and 25 percent being written to. The two primary PC card interface types are ATA and Linear. PC cards that support the ATA interface use an on-card ATA controller, which allows "plug and play" compatibility between portable computers and PDAs. Linear flash cards do not use a dedicated ATA controller and require software drivers to implement file interface protocol.
While flash PC cards can provide sufficient amounts of memory for a broad range of applications, they have not been widely accepted for use in applications such as mobile and portable electronics or for use in applications having significant cost sensitivity. PC cards simply tend to be too large for many portable applications such as pagers, voice recorders, mobile telephones, and hand-held meters. PC cards are also too bulky and heavy for carrying in a pocket or wallet, as would be desirable for many consumer applications. Current PC cards are also quite expensive, hence are offered generally as after market enhancements or add-ons. PC cards can be made available at extremely high memory capacities because of improved memory technology; however, such extremely high memory capacities are in excess of what is optimal for many mobile and portable applications. Moreover, although the insertion lifetime of 68-pin PC card connectors, which is about 10,000 cycles, is generally adequate for portable computers and PDAs, it is inadequate for other applications involving more frequent insertion and removal of the storage media than encountered in portable computing. In addition, the high number of pins and the tendency of the narrow deep sockets on the PC cards to collect foreign material increase the probability of failure, especially if the PC cards are not carefully handled. Also, PC cards have parallel busses, which are problematical since they permit multiple signal transitions that cause system noise and interference with wireless RF products. Some PC cards commonly available use channel hot electron flash technology, which because of its inherent high current demands tends to make erase/write programming times lengthy and reduce effective battery lifetimes in mobile and portable applications.
As the PCMCIA standard is not entirely suitable for small portable devices, flash memory recently has been used in a variety of removable devices having smaller form factors than the standard PC card, including, for example, compact flash cards, miniature cards, and solid state floppy disk cards ("SSFDC"). The surface areas of these devices are illustrated at 110, 120 and 130 respectively in FIG. 1.
The compact flash card is a small format flash memory card that was initially announced by SanDisk Corporation in 1994. The form factor of the compact flash card is 36.times.43.times.3.3 mm, and the surface area thereof, which is shown at 110 in FIG. 1, is approximately 1/3 the surface area of the standard PC Card. The card has a 50 pin connector that is a subset of the PC card interface. The card supports the IDE/ATA interface standard by means of an on-card ATA controller IC. Memory capacity in the range of 2 Megabytes to 15 Megabytes is currently available, although greater memory capacity devices are likely to be introduced. Both 5 volt and 3.3 volt power supplies are supported. A compact flash card is interfaced to notebook computers and PDAs by inserting the card into a special PC card adapter. The compact flash series is described in a publication of the SanDisk Corporation entitled Compact flash Series Preliminary Data Sheet, Document No. 80-11-00015, Rev. 1.0, October 1994.
The miniature card is a small format card that was initially announced by Intel Corporation in 1995. The form factor of the miniature card is 35.times.33.times.3.5 mm, and the surface area, which is shown at 120 in FIG. 1, is approximately 25% the surface area of the standard PC card. The miniature card has a 60 pin Elastimeric connector rated at a minimum insertion lifetime of 5,000 cycles. The card supports a linear addressing range of up to 64 Megabytes of memory using a 16-bit data bus. Memory capacity in the range of 2 Megabytes to 4 Megabytes is currently available, although greater memory capacity devices are likely to be introduced. The miniature card specification allows for flash, DRAM and ROM memory types. Both 5 volt and 3.3 volt power supplies are supported by the specification. A miniature card is interfaced to notebook computers and PDAs that support the standard PC card interface with a special PC card adapter. A miniature card specification is described in Miniature Card Specification, Release 1.0, February 1996, available from Intel Corporation of Santa Clara, Calif.
The solid state floppy disk card, or SSFDC, is a small format card initially announced by Toshiba Corporation in 1995. The form factor of the SSFDC card is 45.times.37.times.0.76 mm, and the surface area thereof, which is shown at 120 in FIG. 1, is approximately 36% the surface area of the standard PC card. The SSFDC has 22 flat contact pads, some of which are I/O pads for both address and data input and output as well as for command inputs. The card specification is dedicated to byte serial NAND-type flash memory. Memory capacity of 2 Megabytes is currently available, although memory capacity in the range of 512 kilobytes to 8 Megabytes is anticipated. The specification accommodates 5 volt or 3.3 volt power supplies. An SSFDC is interfaced to notebook computers and PDAs that have the standard PC card interface with a special PC card adapter. An illustrative device is type TC5816ADC, which is described in Preliminary TC5816ADC Data Sheet No. NV16030496, April 1996, available from Toshiba America Electronic Components, Inc. of Irvine, Calif. The device is said to be suitable for such applications as solid state file storage, voice recording, image file memory for still cameras, and other systems which require high capacity, non-volatile memory data storage.
Seimens Components of Cupertino, Calif. has described a device known as MultiMediaCards, or MMC; see Portable Design, July 1996, p. 23 et seq. The form factor of the MMC package is 37.times.45.times.1.4 mm, and the surface area, which is shown at 140 in FIG. 1, is approximately 36% that of the standard PC card. The MMC package has 6 edge-mounted contact pads with an insertion lifetime of 10,000 cycles, and uses a serial bus. Initially, MMCs are expected to be offered with a choice of 16 Megabit or 64 Megabit ROM memory, but is reported to be teaming up with undisclosed partners to put flash memory on its MMC cards. The specification accommodates a 3.3 volt power supply. The device is said to be suitable for such applications as video games, talking toys, automobile diagnostics, smart phones (tailored operating systems or special programs), PDAs (tailored operating systems or special programs), and notebooks through a PDA adapter.
Some low memory capacity card formats have enjoyed a measure of success in certain specific applications. FIG. 2 shows form factors 210 and 220 of two commercially successful low memory bandwidth card formats known as the IC card format and the SIM card format, respectively. The form factors 210 and 220 are to scale with the form factors 100, 110, 120 and 130 of FIG. 1.
The Integrated Circuit (IC) card format and the similar Identification (ID) card format, commonly known as smart cards, were introduced in the mid 1980's, and have been standardized by the International Organization for Standardization (ISO); see International Organization for Standardization, Identification Cards--Integrated Circuit Cards with Contacts, Part 1: Physical Characteristics, Document No. ISO 7816-1, July 1987; International Organization for Standardization, Identification Cards--Integrated Circuit Cards with Contacts, Part 2: Dimensions and Location of Contacts, Document No. ISO 7816-2, May 1988; and International Organization for Standardization, Identification Cards--Integrated Circuit Cards with Contacts, Part 3: Electronic Signals and Transmission Protocols, Document No. ISO 7816-3, September 1989. Smart cards are credit card sized and typically contain a microcontroller with a small amount of EEPROM memory, typically 256 to 8K bits. The surface area of the smart card is shown at 210 in FIG. 2. The length and width of the smart card is nearly identical with the length and width of the PC card, but the smart card is much thinner. The cards are popular in Europe and are making inroads into the US market. Primary applications are smart telephone calling cards and stored value cards, the later application being promoted by credit card companies like Visa and Master card as a replacement for paper currency. IC and ID cards have a simple contact pattern of eight flat contact pads designated C1-C8 of which only six are used. Contact signal assignments are C1=V.sub.CC (supply voltage), C2=RST (reset), C3=CLK (clock signal), C4=Reserved, C5=GND (ground), C6=V.sub.PP (programming voltage), C7=I/O (data input/output) and C8=Reserved. Due to their popularity in Europe, a great infrastructure of connectors and readers is already established for IC and ID cards.
Another low memory capacity card format is known as the Subscriber Identification Module ("SIM"), which is used in conjunction with mobile telephones based on the Global System for Mobile Communications ("GSM") standard. The SIM specification is set forth in a publication of the European Telecommunication Standard Institute entitled European Digital Cellular Telecommunication System, Global System for Mobile Communications, Phase 2: Specification of Subscriber Identity Module--Mobile Equipment Interface, Document No. GSM11.11, Reference (RE/SMG)-091111PR3, ICS 33.060.50, December 1995. The form factor of the SIM is 25 mm.times.15 mm.times.0.76 mm, and the surface area thereof, which is shown at 220 in FIG. 2, is much smaller than the standard PC card. SIMs offer only a very limited amount of memory, typically less than one kilobit. However, this small amount of memory is sufficient to provide a GSM mobile phone with secure identification of the GSM subscriber, and may also hold a small amount of data for call metering, phone number storage, and in some cases very short data messages (less than a few hundred bytes of data). The SIM uses the same 8 pad contact pattern as the IC card, but only five of the pads are required for V.sub.CC, RST, CLK, GND, and I/O. The plug-in SIM typically is housed in a small hinged smart card connector similar to the type CCM03 available from ITT Cannon Corporation of Santa Ana, Calif. The small form factor allows the GSM SIM to be placed inside the phone as a plug-in module. Because the GSM SIM typically is removed only if a different GSM phone is to be used, GSM SIM connectors typically are designed for fewer insertion/removal cycles than normally experienced with IC and ID cards.
Other memory technologies have not been widely used in insertable/removable memory modules and cards because of their inherent shortcomings relative to such successful technologies as flash. For example, battery-backed SRAM or DRAM memories require supplemental battery power when the main power is removed, while flash memory is non-volatile (no battery is needed) and is more reliable over temperature. Flash memory is available in higher densities and at lower cost/bit than SRAM and EEPROM memory, and is cost-competitive with DRAM memory.
Despite advances in the art, a need still exists for a memory card or module that can store and be used to transfer large amounts of digital information such as commonly encountered in audio, data and image applications, yet be inexpensive to manufacture, compatible with existing standards, easy to store, convenient to insert and remove from its host, rugged and durable enough to withstand numerous insertion/removal cycles, and require minimal hardware interface overhead.